High sensitivity resist compositions for electron-based lithography

ABSTRACT

The resist compositions having an acid sensitive imaging polymer and a radiation sensitive acid generator component comprising: (i) a first radiation sensitive acid generator selected from the group consisting of dissolution-inhibiting acid generators, and (ii) a second radiation sensitive acid generator selected from the group consisting of unprotected acidic group-functionalized acid generators and acid labile group-protected acidic group-functionalized radiation sensitive acid generators; enables formation of high sensitivity resists suitable for use in EPL, EUV, soft x-ray, and other low energy intensity lithographic imaging applications. The resist compositions may be useful in other lithographic processes as well.

BACKGROUND OF THE INVENTION

In the field of semiconductor manufacturing, there is a continued questfor device size shrinkage. This course has led to demands forlithographic techniques to produce smaller feature sizes.

In lithographic processes using wave radiation (e.g., ultraviolet, deepultraviolet (248 nm-KrF), far ultraviolet (193 nm-ArF), the smallestfeature size that can be resolved is related to the wavelength of theimaging radiation. Real use of 193 nm lithographic processes is juststarting in the microelectronics industry. Lithographic processes andtools using 157 nm radiation are envisioned, but are still years fromcommercial implementation. To some extent, feature size resolution witha given imaging radiation wavelength can be enhanced using alternativetechniques such as bilayer lithographic processes and/or mask-relatedlithographic techniques (e.g., phase shift masks, etc.) Nevertheless, itis anticipated that further resolution enhancement capability (e.g.,below 50 nm) will be needed for so-called next generation lithography orNGL. The likely routes for NGL are (a) so-called extreme ultraviolet(EUV) radiation lithography, (b) soft x-ray lithography, (c) electronprojection lithography (EPL).

Electron beam imaging has been used in the microelectronics industry formany years in the manufacture of masks for conventional photolithographyand for low volume/low throughput direct-write wafer applications. Inthese uses, a relatively high energy, narrow electron beam is directedprecisely to selected areas of a resist layer on a mask blank orsemiconductor wafer. Mask-making/direct-write processes are generallyquite slow enabling accurate control of the beam position as it writesthe desired pattern across the resist surface and sufficient energytransfer to the desired portions of the resist layer for subsequentdevelopment of the exposed pattern. Examples of resist materials highlysuitable for use in these electron beam processes are disclosed in U.S.Pat. Nos. 6,043,003 and 6,037,097, the disclosures of which areincorporated herein by reference.

Electron projection lithography (EPL) for NGL is discussed in U.S. Pat.Nos. 4,554,458; 5,866,913; 6,069,684; 6,296,976; and 6,355,383, thedisclosures of which are incorporated herein by reference. As in aconventional lithographic process, EPL involves patternwise exposure ofa resist layer to imaging radiation by projecting the imaging radiationthrough a patterned mask. In the case of EPL, the electron projectionradiation is the imaging radiation. The exposure (optionally followed bybaking) induces a chemical reaction in the exposed portions of theresist which changes the solubility of the exposed regions of theresist. Thereafter, an appropriate developer, usually an aqueous basesolution, is used to selectively remove the resist either in the exposedregions (positive-tone resists) or, in the unexposed region(negative-tone resists). The pattern thus defined is then imprinted onthe wafer by etching away the regions that are not protected by theresist with a dry or wet etch process.

Unfortunately, EPL provides a low intensity imaging radiation such thathigh throughput needed for commercial semiconductor manufacture cannotbe achieved with the resist materials currently available. EUVlithography and soft x-ray lithography have similar problems due to thelack of intensity of the imaging radiation. Typically, the conventionalresist materials lack sufficient sensitivity, exposure dose latitude,stability (e.g., shelf-life, resistance to phase separation, stabilityupon vacuum exposure, etc.). Thus, there is a need for new resistcompositions that can be used for EPL, EUV, soft x-ray, and other lowenergy intensity lithographic imaging applications.

SUMMARY OF THE INVENTION

The invention provides improved resist compositions and lithographicmethods using the resist compositions of the invention. The resistcompositions of the invention are acid-catalyzed resists which arecharacterized by the presence of a radiation sensitive acid generatorcomponent comprising:

-   (i) a first radiation sensitive acid generator selected from the    group consisting of dissolution-inhibiting acid generators, and-   (ii) a second radiation sensitive acid generator selected from the    group consisting of unprotected acidic group-functionalized acid    generators and acid labile group-protected acidic    group-functionalized radiation sensitive acid generators.    The combination of acid generators generally enables formation of    high sensitivity resists suitable for use in EPL, EUV, soft x-ray,    and other low energy intensity lithographic imaging applications.    The resist compositions may be useful in other lithographic    processes as well.

In one aspect, the invention encompasses a resist composition, thecomposition comprising:

-   -   (a) an imaging polymer, and    -   (b) a radiation sensitive acid generator component, the        radiation sensitive acid generator component comprising:        -   (i) a first radiation sensitive acid generator selected from            the group consisting of dissolution-inhibiting acid            generators, and        -   (ii) a second radiation sensitive acid generator selected            from the group consisting of unprotected acidic            group-functionalized generators and acid labile            group-protected acidic group-functionalized acid generators.

The imaging polymer preferably comprises a ketal-functionalized acidsensitive polymer. The second acid generator preferably comprises anacidic moiety selected from the group consisting of phenolic, carboxylicand fluoroalcohol acidic moieties. The resist composition preferablycontains at least about 4 wt. % of the radiation sensitive acidgenerator component based on the weight of the imaging polymer.

In another aspect, the invention encompasses a method of forming apatterned material structure on a substrate using the resist compositionof the invention, the method comprising:

-   -   (A) providing a substrate with a layer of the material,    -   (B) applying a resist composition of the invention to the        substrate to form a resist layer on the substrate;    -   (C) patternwise exposing the substrate to radiation whereby acid        is generated by the acid generator of the resist in exposed        regions of the resist layer by the radiation,    -   (D) contacting the substrate with an aqueous alkaline developer        solution, whereby the exposed regions of the resist layer are        selectively dissolved by the developer solution to reveal a        patterned resist structure, and    -   (E) transferring resist structure pattern to the material layer        by etching into the material layer through spaces in the resist        structure pattern.        The imaging radiation is preferably electron projection, EUV or        soft x-ray radiation. The material to be patterned is preferably        selected from the group consisting of organic dielectrics,        semiconductors, ceramics and metals.

These and other aspects of the invention are discussed in further detailbelow.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides improved resist compositions and lithographicmethods using the resist compositions of the invention. The resistcompositions of the invention are acid-catalyzed resists which arecharacterized by the presence of a radiation sensitive acid generatorcomponent comprising:

-   (i) a first radiation sensitive acid generator selected from the    group consisting of dissolution-inhibiting acid generators, and-   (ii) a second radiation sensitive acid generator selected from the    group consisting of unprotected acidic group-functionalized acid    generators and acid labile group-protected acidic    group-functionalized acid generators.    The combination of acid generators generally enables formation of    high sensitivity resists suitable for use in EPL, EUV, soft x-ray,    and other low energy intensity lithographic imaging applications.    The resist compositions may be useful in other lithographic    processes as well. The invention also encompasses methods of using    these resists to pattern materials.

The resist compositions of the invention generally comprise:

-   -   (a) an acid-sensitive imaging polymer, and    -   (b) a radiation sensitive acid generator component comprising:        -   (i) a first radiation sensitive acid generator selected from            the group consisting of dissolution-inhibiting acid            generators, and        -   (ii) a second radiation sensitive acid generator selected            from the group consisting of unprotected acidic            group-functionalized acid generators and acid labile            group-protected acidic group-functionalized acid generators.

The invention is not limited to any specific acid-sensitive imagingpolymer. The acid-sensitive imaging polymer is preferably a polymerhaving (a) pendant acid labile protecting groups which inhibitsolubility of the resist in aqueous alkaline solutions, and (b) pendantpolar groups (e.g., hydroxyl, carboxyl, fluoroalcohol, etc.) whichpromote the solubility of the resist composition in aqueous alkalinesolutions. Preferred acid-labile protecting groups comprise an acidlabile moiety selected from the group consisting of tertiary alkyl (orcycloalkyl) carboxyl esters (e.g., t-butyl, methyl cyclopentyl, methylcyclohexyl, methyl adamantyl), ketals, and acetals. More preferably, theacid labile moiety is a ketal, most preferably a cyclic aliphatic ketalsuch as methoxycyclopropanyl, ethoxycyclopropanyl, butoxycyclohexanyl,methoxycyclobutanyl, ethoxycyclobutanyl, methoxycyclopentanyl,ethoxycyclopentanyl, methoxycyclohexanyl, ethoxycyclohexanyl,propoxycyclohexanyl, methoxycycloheptanyl, methoxycyclooctanyl ormethoxyadamantyl. Preferred imaging polymers are those described in U.S.Pat. Nos. 6,037097 and 6,043,003, the disclosures of which areincorporated herein by reference.

The radiation acid generator component comprises a combination ofradiation sensitive acid generators. The first radiation sensitive acidgenerator is selected from the group consisting ofdissolution-inhibiting acid generators. These acid generators aredissolution-inhibiting in the absence of the imaging radiation needed tocause acid formation. Dissolution-inhibiting acid generators aregenerally characterized by the absence of (a) acidic functional groups,and (b) acid labile group-protected acidic functional groups. Examplesof suitable radiation-sensitive dissolution-inhibiting acid generatorsinclude the versions of the following acid generators which do not have(a) acidic functional groups, and (b) acid labile group-protected acidicfunctional groups: onium salts such as triaryl sulfoniumhexafluoroantimonate, diaryliodonium hexafluoroantimonate,hexafluoroarsenates, triflates, perfluoroalkane sulfonates (e.g.,perfluoromethane sulfonate, perfluorobutane, perfluorohexane sulfonate,perfluorooctane sulfonate etc.), sulfonate esters of hydroxyimides,N-sulfonyloxynaphthalimides (N-camphorsulfonyloxynaphthalimide,N-pentafluorobenzenesulfonyloxynaphthalimide), a-a′ bis-sulfonyldiazomethanes, naphthoquinone-4-diazides, alkyl disulfones and others. Apreferred dissolution inhibiting acid generator is triphenyl sulfoniumtriflate. The invention is not limited to any specificdissolution-inhibiting acid generator.

The second radiation sensitive acid generator is selected from the groupconsisting of unprotected acidic group-functionalized acid generatorsand acid labile group-protected acidic group-functionalized acidgenerators. The second acid generator, in its unprotected state,promotes solubility of the resist in aqueous alkaline solutions. Theacidic group-functionalized acid generators preferably have an acidicfunctional group having a pKa of about 13 or less, more preferably about10 or less. The acidic functional group is preferably selected from thegroup consisting of phenolic moieties, carboxylic moieties andfluoroalcohol moieties. The acid labile group-protected acidicgroup-functionalized acid generators provide an acidic functionality(preferably selected from the group consisting of phenolic moieties,carboxylic moieties and fluoroalcohol moieties) upon reaction with anacid. Examples of acid labile group-protected acidicgroup-functionalized acid generators are disclosed in U.S. Pat. Nos.5,374,504 and 5,191,124, the disclosures of which are incorporatedherein by reference. A preferred second acid generator is dimethyl(3,5-dimethyl)-4-hydroxyphenyl sulfonium perfluorobutane sulfonate, thestructure of which is shown below:

The resist compositions of the invention will typically contain asolvent prior to their application to the desired substrate. The solventmay be any solvent conventionally used with acid-catalyzed resists whichotherwise does not have any excessively adverse impact on theperformance of the resist composition. Preferred solvents are propyleneglycol monomethyl ether acetate (PGMEA) and cyclohexanone.

The compositions of the invention may further contain minor amounts ofauxiliary components such as dyes/sensitizers, base additives, etc. asare known in the art. Preferred base additives are bases which scavengetrace acids while not having an excessive impact on the performance ofthe resist. Preferred base additives are tertiary alkyl amines, aromaticamines, or tetraalkyl ammonium hydroxides such as t-butyl ammoniumhydroxide (TBAH). Preferably, the unexposed resist compositions of theinvention are substantially insoluble in aqueous alkaline solutionscommonly used to develop lithographic images.

The resist compositions of the invention preferably contain about 0.5-20wt. % (based on total weight of imaging polymer in the composition) ofthe acid generator component more preferably about 4-20 wt. %, mostpreferably about 7-20 wt. %. The weight ratio of first to second acidgenerators is preferably about 5:1 to 1:5, more preferably about 3:1 to1:3, most preferably about 2:1 to 1:2. The acid generator componentpreferably results in a resist composition having an imaging energy doserequirement for high KeV (e.g., about 50-200 KeV) electron sources ofless than about 15 μC/cm², more preferably less than about 10 μC/cm²,most preferably less than about 5 μC/cm². For low KeV (e.g., about 500eV-10 KeV) electron sources, the resist preferably has an imaging energydose requirement of less than about less than about 2 μC/cm², morepreferably less than about 1 μC/cm². For radiation sources such as EUV,the resist compositions of the invention preferably have an imagingenergy dose requirement of less than about 5 mJ/cm², more preferablyless than about 2 mJ/cm², more preferably less than about 1 mJ/cm².Where a solvent is present, the overall composition preferably containsabout 50-90 wt. % solvent. The composition preferably contains about 1wt. % or less of said base additive based on the total weight ofpolymeric component.

The resist compositions of the invention can be prepared by combiningthe polymeric component, acid generator and any other desiredingredients using conventional methods. The resist composition to beused in lithographic processes will generally have a significant amountof solvent.

The resist compositions of the invention are especially useful forlithographic processes used in the manufacture of integrated circuits onsemiconductor substrates. The compositions are especially useful forlithographic processes using electron beam projection radiation or otherlow energy intensity sources (e.g., EUV, soft x-ray, etc.). Where use ofother imaging radiation (e.g. mid-UV, 248 nm deep UV, 193 nm UV, orx-ray) is desired, the compositions of the invention can be adjusted (ifnecessary) by the addition of an appropriate dye or sensitizer to thecomposition, reduction in amount of acid generator component, and/or byelimination of moieties which may impact the optical density at certainradiation wavelengths.

The invention encompasses a method of creating a patterned materialstructure on a substrate using the resist composition of the invention,the method comprising:

-   -   (A) providing a substrate with a layer of the material,    -   (B) applying a resist composition of the invention to the        substrate to form a resist layer on the substrate;    -   (C) pattemwise exposing the substrate to radiation whereby acid        is generated by the acid generator of the resist in exposed        regions of the resist layer by the radiation,    -   (D) contacting the substrate with an aqueous alkaline developer        solution, whereby the exposed regions of the resist layer are        selectively dissolved by the developer solution to reveal a        patterned resist structure, and    -   (E) transferring resist structure pattern to the material layer        by etching into the material layer through spaces in the resist        structure pattern.

The material layer of the substrate is preferably selected from thegroup consisting of organic dielectrics, metals, ceramics,semiconductors or other material depending on the stage of themanufacture process and the desired material set for the end product.The material to be patterned may be applied using any suitabletechnique. The substrate is preferably a semiconductor wafer or a glass(e.g., fused quartz) plate.

If desired, an antireflective coating (ARC) may be applied over thematerial layer before application of the resist layer. The ARC layer maybe any conventional ARC which is compatible with acid catalyzed resists,the underlying material layer, subsequent processing, etc.

Typically, the solvent-containing resist composition may then be appliedto the desired substrate using spin coating or other technique. Thesubstrate with the resist coating is then preferably heated(pre-exposure baked) to remove the solvent and improve the coherence ofthe resist layer. The thickness of the applied layer is preferably asthin as possible provided that (a) the thickness is preferablysubstantially uniform, and (b) the resist layer is sufficient towithstand subsequent processing (typically reactive ion etching) totransfer the lithographic pattern to the underlying substrate materiallayer. The pre-exposure bake step is preferably conducted for about 10seconds to 15 minutes, more preferably about 15 seconds to one minute.The pre-exposure bake temperature may vary depending on the glasstransition temperature of the resist.

After solvent removal, the resist layer is then patternwise-exposed tothe desired imaging radiation. Preferably, the imaging radiation is alow intensity energy source such as electron projection radiation, EUVor soft x-ray. The total exposure energy dose (a) for high KeV (e.g.,about 50-200 KeV) electron sources is preferably less than about 15μC/cm², more preferably less than about 10 μC/cm², most preferably lessthan about 5 μC/cm²; (b) for low KeV (e.g., about 500 eV-10 KeV)electron sources, the energy dose is preferably less than about lessthan about 2 μC/cm², more preferably less than about 1 μC/cm²; for EUV,the imaging energy dose is preferably less than about 5 mJ/cm², morepreferably less than about 2 mJ/cm², more preferably less than about 1mJ/cm².

After the desired patternwise exposure, the resist layer is typicallybaked to further complete the acid-catalyzed reaction and to enhance thecontrast of the exposed pattern. The post-exposure bake is preferablyconducted at about 60-175° C., more preferably about 90°-160° C. Thepost-exposure bake is preferably conducted for about 30 seconds to 5minutes.

After post-exposure bake, the resist structure with the desired patternis obtained (developed) by contacting the resist layer with an alkalinesolution which selectively dissolves the areas of the resist which wereexposed to radiation. Preferred alkaline solutions (developers) areaqueous solutions of tetramethyl ammonium hydroxide. Preferably, theresist compositions of the invention can be developed with conventional0.26N aqueous alkaline solutions. The resist compositions of theinvention can also be developed using 0.14N or 0.21N or other aqueousalkaline solutions. The resulting resist structure on the substrate isthen typically dried to remove any remaining developer solvent.

The pattern from the resist structure may then be transferred to thematerial (e.g., organic dielectric, ceramic, metal, semiconductor, etc.)of the underlying substrate. Typically, the transfer is achieved byreactive ion etching or some other etching technique. Any suitableetching technique may be used. In some instances, a hard mask may beused below the resist layer to facilitate transfer of the pattern to afurther underlying material layer or section. Examples of such processesare disclosed in U.S. Pat. Nos. 4,855,017; 5,362,663; 5,429,710;5,562,801; 5,618,751; 5,744,376; 5,801,094; 5,821,469, and 5,948,570,the disclosures of which patents are incorporated herein by reference.Other examples of pattern transfer processes are described in Chapters12 and 13 of “Semiconductor Lithography, Principles, Practices, andMaterials” by Wayne Moreau, Plenum Press, (1988), the disclosure ofwhich is incorporated herein by reference. It should be understood thatthe invention is not limited to any specific lithography technique ordevice structure.

EXAMPLE 1 Synthesis of dimethyl (3,5-dimethyl)-4-hydroxyphenyl sulfoniumperfluorobutane sulfonate (DMPHS PFBUS)

8 ml of Eaton's Reagent (from Aldrich, 7.7 wt. % of P₂O₅ inmethanesulfonic acid) through an addition funnel to a mixture of 2.44 g(0.02 mol) of 2,6-dimethylphenol and 1.56 g (0.02 mol) ofdimethylsulfoxide in a 50-mL 3-necked round bottom flask equipped with athermometer, N₂ inlet and magnetic stirrer. The rate of the addition wasadjusted so that the temperature of the mixture did not rise above 60°C. during addition. After the exotherm had subsided, the reactionmixture was stirred at room temperature for 2 hours and then poured into40 mL of distilled water. The solution was neutralized to pH=7 by addingammonium hydroxide solution. The resulting solution was stirred at roomtemperature for half an hour and then filtered through a filter paper toremove the brown oily side products. The filtrate was added dropwise toa solution of 6.76 g (0.02 mol) of potassium perfluorobutanesulfonate(KPFBuS) in 70 mL water while stirring. The mixture was further stirredovernight. The white precipitate was collected by suction filtration andwashed with water and ether three times. The crude product wasredissolved in 15-20 mL of ethyl acetate. To this solution, 200-300 mgof aluminum oxide (activated, basic) was added. The mixture was rolledon a roller overnight and then filtered through Celite. The filtrate wasprecipitated into 100 mL ether while stirring. The white precipitate wascollected and further washed with ether three times. Final yield: 2.2 g(23%).

EXAMPLE 2 Synthesis of dimethyl phenyl sulfonium perfluorobutanesulfonate (DMPS PFBUS)

A solution of 4.07 g (0.01 mol) of silver perfluorobutane sulfonate in30 ml of nitromethane was added dropwise, at room temperature, to amixture containing 1.24 g (0.01 mol) of thioanisole and 4.26 g (0.03mol) of methyl iodide in 25 ml of nitromethane. The resulting mixturewas stirred at room temperature for 15 hours. The reaction mixture wasfiltered through Celite to remove the white precipitate. The filtratewas concentrated to about 10 ml and then precipitated into 120 ml ofdiethyl ether. The white solid was collected by vacuum filtration. Thecrude product was redissolved in 15-20 mL of ethyl acetate. To thissolution, 200-300 mg of aluminum oxide (activated, basic) was added. Themixture was rolled on a roller overnight and then filtered throughCelite. The filtrate was precipitated into 100 mL ether while stirring.The white precipitate was collected and further washed with ether threetimes. Final yield: 3.64 g (83%). The product was identified as dimethylphenyl sulfonium perfluorobutane sulfonate by NMR spectroscopy.

EXAMPLE 3 Synthesis of methoxycyclohexene (MOCH) protectedpolyvinylphenol (mondisperse polymer)(PHMOCH)

150 g of propylene glycol methyl ether acetate (PGMEA) was added to 50 gof polyvinylphenol (VP5000 from Tomen) with stirring until a clearsolution is obtained. The solution was then combined with approximately35 mg of oxalic acid. After the acid was dissolved, 18.5 g of1-methoxycyclohexene was added to the solution, and the reaction wascarried out at room temperature with stirring overnight. The reactionwas then quenched with 6 g of basic active aluminum oxide. Theprotection level of 25% on phenol group was determined by C¹³ NMR.

EXAMPLE 4 (COMPARISON) Resist with Single Dissolution Inhibiting AcidGenerator (TPS TRF)

Resist formulations were obtained by mixing the partially protectedpolymer, PHMOCH from Example 3, with 0.14 wt. % (relative to thepolymer) tetrabutyl ammonium hydroxide (TBAH), 0.7 wt. %triphenylsulfonium triflate (TPS TRF) and 200-400 ppm of FC-430surfactant (3M Company) in PGMEA solvent. The total solid weight contentin the solution was about 12%. Similar formulations were made with theloadings of TPS TRF shown in the table below. The resists were spincoated onto respective HMDS-primed wafers. The coated wafers were bakedon a hot plate at 110° C. for 1 minute. The resist was then exposed onIBM-built high throughput e-beam projection system at 75 kV. Afterexposure, the resists were baked at 110° C. for 1 minute before beingdeveloped with 0.263 N TMAH for 60s. The following table lists the dosesto resolve 100 nm line/space images with different TPS TRF loadings.

TPS TRF Dose to resolve loading 100 nm l/s Image profile 0.7 wt. % 40μC/cm² Straight 1.4 wt. % 24 μC/cm² Straight   3 wt. % 12 μC/cm²Straight   5 wt. %  9 μC/cm² Slight foot   6 wt. %  7 μC/cm² Undercutprofile   7 wt. %  5 μC/cm² Phase segregation on the coated film

EXAMPLE 5 (COMPARISON) Resist with Single Dissolution Promoting AcidGenerator

Resist formulations were obtained in the manner of Example 4 except thatDMPHS PFBUS of Example 1 was substituted for TPS TRF. The loading ofDMPHS PFBUS is indicated in the table below based on the weight of theimaging polymer. The resists were spin coated onto respectiveHMDS-primed wafers. The wafers were baked on a hot plate at 110° C. for1 minute. The resist-coated wafers were exposed at 25 kV onElectronCure™-200M flood exposure tool manufactured by Electron VisionGroup. After exposure, resists were baked at 110° C. for 1 minute beforebeing developed with 0.263 N TMAH for 60s. The following table lists thedoses to clear large square exposed with different DMPHS PFBUS loadings.

DMPHS PFBUS loading E₀, dose to clear 0.82 wt. %  12 μC/cm² 3.28 wt. %  4 μC/cm² 4.91 wt. %   3 μC/cm² 6.55 wt. % 2.5 μC/cm² 8.19 wt. % 2.1μC/cm² 12.28 wt. %  1.5 μC/cm² (start to see extra thinning)

EXAMPLE6 Resist with Mixed Acid Generators (DMPS PFBUS and DMPHS PFBUS)According to the Invention

Resist formulations were obtained in the manner of Example 4 except thata combination of DMPHS PFBUS of Example 1 and DMPS from Example 2 wassubstituted for TPS TRF. The loading of the acid generators is indicatedin the table below based on the weight of the imaging polymer.

The resists were spin coated onto respective HMDS-primed wafers. Theresist-coated wafers were baked on a hot plate at 110° C. for 1 minute.The resist-coated wafers were exposed using an IBM-built 25 kVGaussian-beam system (FELS). After exposure, resists were baked at 110°C. for 1 minute before being developed with 0.263 N TMAH for 60s. Thefollowing table lists the doses to resolve 150 nm l/s images withdifferent DMPS PFBUS and DMPHS PFBUS loadings and image profiles.

DMPS DMPHS Dose to PFBUS PFBUS resolve Image Sample loading loading 100nm l/s profile 2x DMPS 1.49 wt. %   0 wt. % 4.5 μC/cm²   undercut (1/0)(comparison) Mix a (3/1) 0.56 wt. % 0.82 wt. % 5 μC/cm² square andstraight Mix b (1/1) 0.74 wt. % 1.64 wt. % 5 μC/cm² square and straightMix c (1/3) 0.37 wt. % 2.45 wt. % 5 μC/cm² square and straight 4x DMPHS  0 wt. % 3.27 wt. % 5 μC/cm² slightly (0/1) rounding (comparison) ontop

EXAMPLE 7 Resist with Mixed Acid Generators (TPS TRF and DMPHS PFBUS)According to the Invention

Resist formulations were obtained in the manner of Example 4 except thata combination of DMPHS PFBUS of Example 1 and TPS TRF was substitutedfor TPS TRF. The loading of the acid generators is indicated in thetable below based on the weight of the imaging polymer. The resists werespin coated onto respective HMDS-primed wafers. The resist-coated waferswere baked on a hot plate at 110° C. for 1 minute. The resist-coatedwafers were exposed using an IBM-built 25 kV Gaussian-beam system(FELS). After exposure, resists were baked at 110° C. for 1 minutebefore being developed with 0.263 N TMAH for 60s. The following tablelists profiles for 150 nm and 200 nm l/s images with different TPS TRFand DMPHS PFBUS loadings at both 1.5 μC/cm² and 2.0 μC/cm².

DMPHS Image Image TPS TRF PFBUS profile at profile at Sample loadingloading 1.5 μC/cm² 2.0 μC/cm² 8x TPS TRF 5.6 wt. %   0 wt. % undercutundercut (1/0) (comparison) Mix d (3/1) 4.2 wt. % 3.28 wt. % slightlyslightly undercut undercut Mix e (1/1) 2.8 wt. % 6.55 wt. % square andsquare and straight straight Mix f (1/3) 1.4 wt. % 9.83 wt. % square andslightly straight rounding and straight 16x DMPHS   0 wt. % 13.10 wt. % severe severe PFBUS (0/1) rounding and rounding and (comparison) filmloss film loss

EXAMPLE 8 Optimized Formulation

A study of resist performance characteristics (e.g., dose latitude,resist profile as related to unexposed dissolution, sensitivity, andE₀/E_(CD)) was performed to determine an optimal composition using theimaging polymer of Example 3 and the combination of acid generators ofExample 7. From this study, it appears that a composition having 0.28wt. % TBAH, 7 wt. % TPS TRF and 7.37 wt. % DMPHS PFBUS provided the bestoverall performance (31% dose latitude, 7.4 Å/second unexposeddissolution rate, an E₀/E_(size) of 0.74, and a sensitivity of 3.9mC/cm² with vertical resist profiles).

Wafers coated with this formulation in the manner of Example 4 were thenimaged on a soft x-ray (1.1 nm wavelength) lithography tool from JMARTechnologies Inc. Using soft x-ray, the resist of the invention requireda dose of less than 15 mJ/cm². Commercial resists would have an exposuredose requirement in the range of 50-90 mJ/cm² for the same soft x-rayexposure process.

1. A resist composition comprising (a) an imaging polymer, and (b) aradiation sensitive acid generator component, said radiation sensitiveacid generator component comprising: (i) a first radiation sensitiveacid generator selected from the group consisting ofdissolution-inhibiting acid generators, and (ii) a second radiationsensitive acid generator selected from the group consisting ofunprotected acidic group-functionalized radiation sensitive acidgenerators.
 2. The resist composition of claim 1 wherein said imagingpolymer comprises a ketal-functionalized acid sensitive polymer.
 3. Theresist composition of claim 1 wherein said second radiation-sensitiveacid generator is an acidic group-functionalized acid generatorcomprising an acidic moiety selected from the group consisting ofphenolic moieties, carboxylic moieties and fluoroalcohol moieties. 4.The composition of claim 1 wherein said resist composition contains atleast about 4 wt. % of said radiation sensitive acid generator componentbased on the weight of said imaging polymer.
 5. The composition of claim1 wherein said first and second acid generators are present in a moleratio of about 5:1 to about 1:5.
 6. A method of forming a patternedmaterial structure on a substrate, said material being selected from thegroup consisting of organic dielectrics, semiconductors, ceramics andmetals, said method comprising: (A) providing a substrate with a layerof said material, (B) applying a resist composition to said substrate toform a resist layer on said substrate, said resist compositioncomprising an imaging polymer and a radiation sensitive acid generatorcomponent, said radiation sensitive acid generator component comprising:(i) a first radiation sensitive acid generator selected from the groupconsisting of dissolution-inhibiting acid generators, and (ii) a secondradiation sensitive acid generator selected from the group consisting ofunprotected acidic group-functionalized radiation sensitive acidgenerators, (C) patternwise exposing said substrate to radiation wherebyacid is generated by acid generator of the resist in exposed regions ofsaid resist layer by said radiation, (D) contacting said substrate withan aqueous alkaline developer solution, whereby said exposed regions ofsaid resist layer are selectively dissolved by said developer solutionto reveal a patterned resist structure, and (E) transferring resiststructure pattern to said material layer, by etching into said materiallayer through spaces in said resist structure pattern.
 7. The method ofclaim 6 wherein at least one intermediate layer is provided between saidmaterial layer and said resist layer, and step (E) comprises etchingthrough said intermediate layer.
 8. The method of claim 6 wherein saidradiation is selected from the group consisting of electron projectionradiation, EUV radiation, and soft x-ray radiation.
 9. The method ofclaim 6 wherein said substrate is baked between steps (C) and (D). 10.The method of claim 6 wherein said imaging polymer comprises aketal-functionalized acid sensitive polymer.
 11. The method of claim 6wherein said second radiation-sensitive acid generator is an acidicgroup-functionalized acid generator comprising an acidic moiety selectedfrom the group consisting of phenolic moieties, carboxylic moieties andfluoroalcohol moieties.
 12. The method of claim 6 wherein said resistcomposition contains at least about 4 wt. % of said radiation sensitiveacid generator component based on the weight of said imaging polymer.13. The method of claim 6 wherein said first and second acid generatorsare present in a mole ratio of about 5:1 to about 1:5.
 14. Thecomposition of claim 1 wherein said second radiation-sensitive acidgenerator is dimethyl (3,5-dimethyl)-4-hydroxyphenyl sulfoniumperfluorobutane sulfonate.